Abstract

Characterization of n-type GaAs, etched in a 5:1:1 mixt. of H2SO4:H2O2:H2O, was performed using XPS and electrochem. a.c. impedance. Quant. XPS anal. of GaAs indicated that the as-received wafers had a gallium-rich native oxide which was not affected by solvent degreasing treatment. Subsequent, oxidative etching formed a thinner arsenic-rich oxide. It is suggested that etching causes initial thinning of the native oxide; subsequently, transport of Ga and As ions occurs through the film by high-field ionic conduction. Arsenic enrichment in the resultant oxide film arises from the greater mobility of Ga3+ ions compared with As3+ ions as well as the relative soly. of Ga2O3 compared with As2O3. The as-received oxide film thickness, detd. from the ratio of the oxide to substrate XPS peaks, was approx. 1.1 nm. After etching, this was reduced to about 0.7 nm. This thickness is consistent with the driving voltage for oxide formation being provided by the electrochem. p.d. between hydrogen peroxide and the GaAs wafer (i.e. between 0.4 V, for As, and 1.2 V, for Ga, at a nm V-1 ratio of 2). Capacitance measurements, derived from electrochem. impedance data, combined with film thickness data, gave a value of about 5 for the dielec. const. of As2O3. [on SciFinder (R)]

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